Telecommunications systems employ Digital Speech Interpolation (DSI) equipment to process digital speech signals that will be transmitted/received over particular transmission media, e.g., optical fiber. Such processing includes compressing the digital speech signals before they are transmitted over the transmission media. It also includes removing noise signals that may be present between speech words, i.e., during silent periods/pauses as shown in FIG. 1A. For example, FIG. 1A depicts the original signal that includes bursts of speech signals "a" having noise signal "c" superimposed on the speech signals. The noise signal is also present during silent intervals as shown at "b". Such noise signals are removed from the signal stream to achieve more efficient use of the transmission media, and, therefore, are not transmitted, except for those noise signals that are superimposed on the speech signals. When the compressed result is received at the opposite end of the connection, equipment thereat decompresses the speech signals and inserts a locally manufactured noise signal referred to as "comfort noise", e.g., a white noise signal, during such pauses in the signal stream. The receiving equipment thus manufactures and inserts the noise signals into the signal stream to simulate a typical telephone connection, as is illustrated in FIG. 1B. Specifically, the receiving equipment decompresses the signal information that it receives and outputs the result as depicted by speech signals "a". If noise signals were superimposed on speech signals, then that effect is also produced at the receiving end, as represented by signal level "c". Thus, segment "c" of the reconstructed waveform represents a composite of speech signal, signal "a", and the superimposed noise, signal "c". The receiving equipment also manufactures a predetermined level of comfort noise and inserts this during pauses in the signal stream, as depicted at "d".
I have recognized, however, that as a result of the foregoing technique the receiving party hears two different, distinct noise signals--the comfort noise and the noise superimposed on the speech signals--which the receiving party may find disconcerting, especially if the superimposed noise signal contains an appreciable level of energy. For example, if a call is being made from a very noisy environment, e.g., an airport, then it is likely that background noise having an appreciable level of energy will also be transmitted over the telephone connection. It is likely that such background noise will also be superimposed on the speech signals that will be heard by the receiving party positioned at the opposite end of the connection. The receiving party will thus hear a high level noise signal with the speech signals, but then hear a very low level comfort noise during pauses in the speech.